Major ocular components of an eye include a retina and cornea. The cornea connects to the sclera at the limbus. An anterior segment of the eye is divided into two principle chambers by the iris and pupil. An anterior chamber is defined by the space between the cornea and the iris. A posterior chamber is defined by the space between the iris and vitreous.
A natural crystalline lens is located behind the pupil as defined by the iris. The natural crystalline lens is attached at its periphery by zonules. The eye is deformable and the zonule attachments allow the natural crystalline lens to deform to different optical powers. In some cases, the natural crystalline lens does not properly deform to achieve a required focus or the length of the eyeball is such that an image does not fall directly on the retina. Spectacles or contact lenses are required to compensate for the focus of the natural lens or axial length of the eye. Recent technological developments have provided a deformable and relatively permanent artificial intraocular lens that can be implanted into the eye to provide permanent vision correction. An intraocular lens has an optical zone portion and is generally made of flexible material suitable for optical use such as silicone.
At least two general problems are associated with implantation of an intraocular lens. First, the implantation method requires a relatively large incision, which can lead to complications such as infection, retinal detachment and laceration of the ocular tissue. A second problem relates to the intraocular environment. Intraocular tissue is extremely delicate and sensitive. Any artificial body that is inserted into the eye must be designed with consideration of the body's interface with intraocular tissue on all surfaces, not just one surface as with an exterior, surface contact lens. Further, intraocular tissue differs from exterior eye tissue. At least one surface of exterior eye tissue is exposed to the hardening influence of an exterior environment, which at least to some extent enures the one surface to the effect of foreign bodies such as a surface contact lenses.
U.S. Pat. Nos. 4,573,998 and 4,702,244 both to Mazzocco, disclose an improved intraocular lens structure, method and instrumentation for implantation through a relatively small incision in ocular tissue. The disclosures of the U.S. Pats. No. 4,573,998 and 4,702,244 are incorporated herein by reference. The lens structure disclosed in the U.S. Pat. Nos. 4,573,990 and 4,702,244 comprises a deformable optical zone portion having prescribed memory characteristics. The lens can be deformed by compressing, rolling, folding, stretching or by a combination thereof to a small diameter for insertion through a small incision in the eye. The memory characteristics enable the lens to return to an original configuration with full size and fixed focal length after insertion. The optical zone portion of the lens is fabricated from a biologically inert material possessing elasticity and compression characteristics.
Copending parent application, Ser. No. 08/318,991 to Feingold addresses a problem of shape of an intraocular lens with regard to the intraocular environment. The disclosure of this application is incorporated herein by reference.
Feingold teaches an intraocular contact lens provided with an outer radius of curvature between a lens body portion (base portion) and a lens portion (optic portion) that smoothly transitions therebetween. Specifically, there exists a transition in the outer radius of curvature of the lens between the lens base portion and the optic portion. It is important that the transition in the radius of curvature between these two portions or zones is such that there is a minimization of edge formation so as to prevent damage or wear to the back of the iris. A transition can be made that has a gradient of radius of curvature within very small dimensions. The transition forms a transition portion that defines an elliptically transcribed surface transition from the surface of the optic portion to the surface of the base portion. Such an arrangement works well within the eye and does not appear to damage or wear the back of the iris.
Feingold also teaches that at least one groove can be provided in the outer surface of the intraocular contact lens. The groove is preferably in the arrangement of a circular groove located in the base portion and surrounding the optic portion. The circular groove allows for good circulation of eye fluid to facilitate lubrication between the intraocular contact lens and the back of the iris. Other groove configurations can be utilized.
Further, Feingold teaches that a passageway can be provided in the intraocular lens between posterior and anterior surfaces to equalize intraocular pressure against the lens surfaces to allow equalization of pressure between anterior and posterior eye chambers. The passageway is provided in a variety of different forms. The passageway can be in the form of a groove in the anterior surface and a groove in the posterior surface that connect to form a continuous channel or the passageway can be provided in the form of a hole through the thickness dimension of the intraocular lens at one or more locations.
Feingold also provides one or more through holes in the iris to place the anterior chamber and posterior chamber in fluid communication to allow equalization of pressure therebetween. This prevents the intraocular contact lens from being sucked into tight contact with the back of the iris to cause damage and wear to the back of the iris. The tight contact effect is due to a differential pressure between the posterior and anterior eye chambers. The through holes eliminate the differential pressure between the chambers.
FIG. 25 is a partial side sectional view of a human eye showing a location of an implanted intraocular contact lens. The lens is located in the posterior chamber and can be fixed in the chamber by a peripheral body member (haptic), which extends beyond the optic portion of the lens. The body member accomplishes fixation by contacting the peripheral tissues of the eye posterior to the iris in the area of the ciliary sulcus. The posterior surface of the lens intimately contacts the convex anterior surface of the lens.
One problem with this arrangement is that the intimate contact between surfaces of the implanted lens and the natural crystalline lens can cause cataracts. It is desirable to place the intraocular lens in a position with respect to the natural lens that minimizes contact between surfaces of the implanted lens and the natural crystalline lens to reduce the risk of cataracts. Heretofore however, it has been believed necessary to intimately contact the two surfaces in order to achieve proper refractive correction. The present invention is based in part on a finding that proper refractive correction can be achieved and at the same time, development of cataracts can be avoided by implanting an intraocular lens so as to form a spacing between the posterior surface of the intraocular lens and the anterior surface of the natural crystalline lens.